PTL 1 discloses a device to obtain a function of facilitating a warm-up operation of an engine in addition to a function as a heater heating air to be blown into a passenger compartment using a coolant, which is heated by an engine, as a heat source and a function as a heater using a high-pressure refrigerant as a heat source.
To accomplish the above specified purpose, the function as a heater heating air to be blown into a passenger compartment using a coolant as a heat source and the function as a heater using a high-pressure refrigerant as a heat source are realized by one heat exchanger (a heater for an air conditioner), and a U-shaped tube, which exchanges heat between the high-pressure refrigerant and the coolant, is disposed in a refrigerant tank. Further, when the temperature of the coolant is low, the coolant is allowed to circulate through the U-shaped tube. When the temperature of the coolant is high, the coolant is allowed to circulate through a coolant tube.
PTL 2 discloses a vehicle air-conditioning apparatus including a heat pump-type refrigerating cycle that improves the heating efficiency when performing a heating operation by using a heating unit, which uses hot water as a heat source, in combination. To accomplish the above specified purpose, a heat exchanger for cooling is disposed on the leeward side of a blower in a duct that guides blown air into a passenger compartment of a vehicle. A heat exchanger for heating and a heater core, which forms a hot water-type heating unit, are disposed on the leeward side of the heat exchanger for cooling. The heater core is supplied with brine, which is heated by a combustion-type hot water heater, by a pump, and heats circumambient air by radiating the heat of the brine into the duct. The heater core is disposed on the leeward side of the heat exchanger for heating, and shares fins with the heat exchanger for heating.
A three-fluid heat exchanger to be described in this disclosure will be described here. A heat exchanger is to generally exchange heat between two media, such as air and refrigerant. However, the three-fluid heat exchanger to be described in this disclosure is a heat exchanger that substantially exchanges heat simultaneously between three media, such as coolant, air, and refrigerant.
Further, the media are not limited to coolant, refrigerant, and air, and are called a first fluid, a second fluid, and a third fluid. Accordingly, the heater core, which shares the fins with the heat exchanger for heating of PTL 2, forms the three-fluid heat exchanger. That is, the three-fluid heat exchanger is well-known.
Further, PTL 3 discloses a vehicle air conditioner with a reduced size that has a rapid heating operation mode using a high-pressure refrigerant. To accomplish the above specified purpose, a function as a heater heating air to be blown into a passenger compartment using an engine coolant as a heat source and a function as a heater using a high-pressure refrigerant as a heat source are realized by one heat exchanger (a heater for an air conditioner).
In PTL 3, when rapid heating is performed, the engine coolant is allowed to circulate between a bypass passage and a heater for an air conditioner and the high-pressure refrigerant is allowed to circulate through the heater for the air conditioner while the inflow of the engine coolant, which has flowed out of the engine, into the heater for an air conditioner is stopped. Accordingly, while the mountability of the air conditioner on the vehicle is improved through the reduction of the size of the air conditioner, rapid heating capacity is improved. The heater for the air conditioner is also the three-fluid heat exchanger to be described in this disclosure, and involves three fluids, such as engine coolant, refrigerant, and air.
A demand for the management of the heat of a vehicle increases when there is increase in the kinds of thermal devices other than an engine in a vehicle. However, particularly, a coolant circuit for a vehicle has a large difference in the increase and decrease of the amount of heat caused by various situations. Accordingly, when a heat exchanger, which is designed and manufactured so as to have required maximum performance, is disposed in a vehicle as each heat exchanger, a very large space is needed and there can be waste of space. Meanwhile, if the waste heat of an automobile is reduced, the amount of heat to be radiated at a normal operation has tendency to be continuously low. However, specific solutions to these issues are not described in PTLs 1 to 3.